Consider this: of the trillions upon trillions of cells in the human body, only about 1 in 10 is actually human. The rest belong to microbes, which colonize every inch of you, from the inside of your mouth to the skin between your toes. It’s no wonder, then, that research is increasingly finding that the diversity of these microbes has important effects on health.

The vast majority of microbes — perhaps up to 100 trillion of them — live in our guts. So-called gut bugs help digest our food, assist our immune systems, maintain the health of the intestines, produce vitamins, aid metabolism and extract calories from food (which is why much research has associated gut bugs with obesity).

To better understand the way gut bugs work, a new study has aimed to categorize the lot of them. The study, led by Peer Bork of the European Molecular Biology Laboratory in Heidelberg, Germany, found that the bacteria in our guts falls into one of three distinct ecosystems, or “enterotypes.”

“The three gut types can explain why the uptake of medicines and nutrients varies from person to person,” Jeroen Raes, a bioinformatician at Vrije University in Brussels and coauthor of the new study, said in a statement. Which means that knowing a person’s enterotype could someday help doctors tailor drug treatments or diets to suit them better.

Or, [Bork] speculated, doctors might be able to use enterotypes to find alternatives to antibiotics, which are becoming increasingly ineffective. Instead of trying to wipe out disease-causing bacteria that have disrupted the ecological balance of the gut, they could try to provide reinforcements for the good bacteria. “You’d try to restore the type you had before,” he said.

For the new study, the research team evaluated stool samples from 22 European individuals, extracted the DNA and determined its composition by using DNA analysis and computers. They also compared the results to other published findings from Japanese and American subjects.

Scientists found that each of the three enterotypes was composed of a unique balance of microbe species. The team named each type after its dominant bacteria: Bacteroides, an enterotype that’s known to break down carbohydrates and is better at making vitamins B2, B5, C and H; Prevotella, which degrades mucus and produces more B1 and folic acid; and Ruminococcus, which helps cells absorb sugars.

People’s enterotypes had no relation to their weight, ethnicity or geographic group. Just like blood or tissue types, the three enterotypes were found all over the globe — or at least in all the regions from which researchers had samples. “You can cut the data in lots of different ways, and you still get these three clusters,” Bork told the Times.

The authors caution that it’s too soon to say concretely how a person’s enterotype affects his or her health. The current study was a huge undertaking, but more testing is needed — in a greater diversity of people — before real medical applications can be introduced, the researchers said.